Understanding the dynamic role of glutamine transport between neuron and astrocyte is crucial to the functional characterization of the glutamine/glutamate cycle and the advancement of our knowledge of glutamate neurotransmission. Although there has been phenomenal progress in the glutamine transport field, the development of selective agents for the manipulation of glutamine concentrations has not been accomplished. Historically, the advance in a discipline of biochemistry has been accompanied by, if not preceded by, a library of important compounds that define that discipline. Understanding glutamine transport is the next obvious step to fully understanding glutamate neurotransmission, and the detailed analysis of glutamine movement will require selective compounds to aid in defining the systems as well as realizing the physiological significance. This proposed research will provide such needed compounds. The overall goal of this project is to provide a detailed description of the binding site of the glutamine transporters ASCT2 and SIM1, and in doing so develop selective agents as tools for the manipulation of glutamine concentrations. These tools will allow closer study of the glutamine/glutamate cycle as well as allow other researchers the ability to design more specific experiments relating to glutamine transport, glutamine metabolism, and the physiological relevance of these processes within the CNS. The strategy to accomplish this is to express the glutamine transporter clones ASCT2, and SN1, and develop selective inhibitors of these systems. The development of the selective inhibitors will incorporate a novel approach of targeting the specific ligand/protein bonding interactions into the molecular design.